at short range i do not believe the shot size matters as to its lethality. a bigger concern is over penatration and what is going to stop it.
absolutely right, though not in the context you mean. Penetration is important. Birdshot tends to make a large surface wound, with little penetration.
If your intent is to wound and maim, then use those #7s. If you want to stop your attacker, use 00 Buck.
My intent is to use my attacker's body to stop the buck shot.
